THE FATIGUE AND VOLUNTARY DISCHARGE PROPERTIES OF SINGLE MOTOR UNITS IN MAN
THE FATIGUE AND VOLUNTARY DISCHARGE PROPERTIES OF SINGLE MOTOR UNITS IN MAN
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DOI：
10.1113/jphysiol.1981.sp013805
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发表时间：
1981-01-01
影响因子：
5.5
通讯作者：
HEDMAN, B
中科院分区：
文献类型：
--
作者：
GRIMBY, L;HANNERZ, J;HEDMAN, B
应用肌电图（EMG）记录研究了长时间最大自主力时单个运动单元的放电特性，主要是大脚趾短伸肌和胫骨前肌。EMG记录的选择性在之前的机械损伤后的短大脚趾伸肌和末梢神经细枝和肌肉纤维以及随之而来的侧支萌发，以及使用高阻抗导线电极在胫骨前肌中实现。在持续最大努力的最初几百毫秒里，运动单元的运动速率从0.0.4%到0.0.4%不等。30-60 Hz，张力与50 Hz以上的脚趾伸肌神经电刺激所获得的张力相同。在长时间的最大努力中，射击率和运动单元射击的比例依次下降。运动单元最初以30赫兹的频率发射，随后继续以15-20赫兹的频率发射。最初以60赫兹放电的运动单元停止了调性放电，但仍然可以进行阶段性放电。通过长期训练，所有运动单元的紧张性反应时间可以从几秒增加到20秒。耐力有限的运动单元在维持收缩的早期比后期以较低的张力发射。可能，支配慢肌纤维的运动神经元以足以完全融合的速率持续响应长时间的随意驱动，但支配快肌纤维的运动神经元的阈值增加，因此它们最终主要是相位放电，从而保护外周兴奋和收缩机制免受过度耗竭。
The discharge properties of single motor units during prolonged maximal voluntary effort were studied using electromyographic [EMG] recordings, mainly in the short big toe extensor muscle and also in the anterior tibial muscle. The required selectivity of the EMG recordings was achieved in the short big toe extensor muscle after previous mechanical lesions to the terminal nerve twigs and muscle fibers and consequent collateral sprouting, and in the anterior tibial muscle with the use of a high impedance wire electrode. During the first few hundred milliseconds of sustained maximal effort the motor units fired at rates ranging from .apprx. 30-60 Hz, and the tension was the same as that obtained on electrical tetanization of the nerve to the toe extensor muscles above 50 Hz. During prolonged maximal effort the firing rates and the proportion of motor units firing successively decreased. Motor units initially firing at 30 Hz continued to fire tonically but at 15-20 Hz. Motor units initially firing at 60 Hz ceased to fire tonically but could still be made to discharge phasically. The period of time during which all motor units responded tonically could be increased from a few seconds up to 20 s by long-term training. Motor units with a limited endurance fired at a lower tension in the early than in the late stages of maintained contraction. Probably, motoneurons innervating slow twitch muscle fibers respond continuously to prolonged voluntary drive at rates sufficient for full fusion, but the threshold of motoneurons innervating fast twitch muscle fibers increases so that they finally mainly fire phasically thus protecting the peripheral excitation and contractile mechanisms from excessive exhaustion.